People expect them. Visitors who can’t find the information they want may look to an FAQ page to quickly find what they want.
Some visitors like FAQ pages. They like finding all the information they want in one spot. (But, this assumes that all that info can fit on one page.)
Reasons to avoid an FAQ page
They are not actually frequently asked questions. If you don't have actual questions asked by actual visitors to your site, don’t include an FAQ page.
Because you have many many questions asked by actual visitors. Having lots of FAQ may simply mean that the rest of the site isn’t addressing user needs. Better site organization is likely to solve this problem.
There are better ways of presenting the content. Infographics, images, or text can likely present the content in a more attractive, easier-to-read fashion.
FAQ often become a junk drawer of all the information that hasn't been organized. Don't ask users to read a list of 20 questions just to find out if their question is answered.
Writing an FAQ Page
Break the page into sections or categories. If there are more than a few questions, consider using anchor links.
Answers should include links to pages with more information on the topic.